Known examples of a conventional inspection method for investigating the presence/absence of a defect in a magnetic member such as thinning or crack encompass (i) magnetization eddy current testing (magnetization ECT (Eddy Current Testing)) disclosed in Patent Literature 1 and the like and (ii) a magnetic flux leakage (MFL) disclosed in Patent Literature 2 and the like.
Known examples of a method of quantitatively measuring a depth or the like of a defect of a magnetic member encompass a submersion rotary ultrasonic thickness measuring method (IRIS; Internal Rotary Inspection Systems).